This invention relates to the art of increasing the filling power of tobacco filler. More particularly, this invention relates to a process whereby the filling power of tobacco filler is increased without the use of exogenous puffing or blowing agents.
During curing, the moisture content of tobacco leaves is greatly reduced resulting in shrinkage of the leaf structure and a decrease in filling power. Additionally, the shredding or cutting techniques generally employed to convert the cured tobacco leaves into filler may result in some lamination and compression of the tobacco, thereby decreasing the filling power even further. Many processes have been devised for increasing the filling power of cured tobacco for reasons well known in the art.
The heretofore known processes may be broadly characterized as involving penetration or impregnation of the tobacco with impregnants (blowing or puffing agents) which when removed during a subsequent expansion process step generate elevated pressure in the tobacco cells to expand the cell walls resulting in an expansion of the tobacco. The impregnant may be a solid, a liquid, or a gas. Most often, such an expansion process involves generating and expanding a gas or, in the case of a gaseous impregnant, simply causing the gas to expand, within the cell, thereby causing expansion of the cell volume. The rate of expansion or generation and expansion of the gas thus has to be greater than the rate at which it is removed by diffusion through the cell walls, but the maximum resulting pressure has to be less than the bursting strength of the cell structural elements.
Among the impregnants which have been employed are pressurized steam, air, water, organic solvents, ammonia, carbon dioxide, combinations of ammonia and carbon dioxide, and compounds capable of liberating a gas when subjected to chemical decomposition, as by heating. Among the means disclosed for removing the impregnant to expand the cell walls are a sudden reduction in pressure, freeze-drying, convection heating, radiant transfer (infrared), and the application of a microwave field.
Impregnants such as water, alcohol, acetone, a volatile hydrocarbon or a volatile halogenated hydrocarbon, which may also be employed as solvents for the gas-releasing compounds, may be applied to the tobacco by spraying, sprinkling or dipping in any desired manner. In such cases, thorough and rapid impregnation may be further assisted if the tobacco is subjected to subatmospheric pressure to expel a portion of the air from the tobacco particle interstices before it is contacted with the impregnating solution. It is generally preferred in the art to incorporate gas-releasing impregnants into the tobacco in the liquid condition in order that uniform impregnation of the tobacco may be achieved, but in certain cases, the gas-releasing chemical may be formed in situ within the tobacco or may be applied to the tobacco in the dry state, e.g., by dusting or otherwise.
While a number of the known processes may be employed to provide a satisfactory expanded tobacco product, which may then be blended with an unexpanded tobacco and formed into cigarettes or the like, the known processes do possess certain disadvantages. Thus, the use of certain impregnants, such as halogenated hydrocarbons, which are foreign to tobacco may not be completely satisfactory, because some of the materials employed are not always desired as additives and the introduction, in considerable concentration, of such foreign materials presents the problem of removing the expansion agent after the treatment has been completed in order to avoid affecting aroma and other properties of the smoke. Moreover, aside from the aforementioned disadvantages, the use of such foreign materials adds to the overall cost of producing tobacco end products.
Processes employing water as an impregnant have tended to produce a more satisfactory result with tobacco stems than with tobacco lamina filler. It may be that the greater permeability of the leaf structure permits the water impregnant to escape before substantial expansion can take place. Removal of the water impregnant by freeze-drying is not only a comparatively slow and expensive approach but may result, in some instances, in a product which has an objectionable amount of tackiness because of the hygroscopicity of a film-like layer of water-extracted solids which forms on the surface of the tobacco. Removal of the water impregnant using a microwave field also requires elaborate and expensive equipment and may tend to be more effective with tobacco stems than with tobacco lamina filler.
Impregnating tobacco with air, carbon dioxide or steam, under pressure, and then suddenly releasing the pressure to expand the tobacco is not generally satisfactory since the volume of the tobacco is only slightly or, at best, only moderately increased, for example, by about 3 to 15 percent. Additionally, the process may result in shattering the tobacco structure and particles so that considerable waste, incident to the formation of fines, results.
One particular difficulty with the impregnation processes in which the impregnant is removed during a subsequent expansion step is that the degree of expansion which results during removal of the impregnant may not be readily controlled. As a consequence, present practice generally requires that tobacco that has been treated to increase its filling capacity, as by being expanded, be blended with unexpanded tobacco. This is undesirable, particularly since it requires an extra blending step and the maintenance of separate storage facilities for the treated and untreated tobacco.
It has now been discovered that tobacco lamina filler may be stiffened and expanded to increase its filling power without the use of an exogenous impregnant by contacting the filler with a heat transfer medium such that heat is rapidly and substantially uniformly transferred from the medium to the filler for a time sufficient to stiffen and expand the filler and that this process is effectively employed with filler having an OV value, before treatment, within the range of from about 8% to about 30%. Among the advantages to be realized are that the degree of expansion may be controlled so that not only increases in cylinder volume in excess of 70% over the unexpanded cylinder volume may be consistently achieved, but also moderate expansion may be selected thus eliminating the need to blend the expanded filler with unexpanded filler, if that is desired. An additional advantage is that the filler expanded according to the process of the present invention is substantially stable in that little, if any, collapse is experienced during reordering. Yet another advantage is that the process may be effectively employed at atmospheric pressure.